The need for preservatives in the cosmetic and allied industries has long been recognized. Among those most commercially acceptable are the esters of p-hydroxybenzoic acid (parabens) and substituted dimethylhydantoin-based products. Their use individually is described by D. N. Maddox, "The Role of p-Hydroxybenzoates in Modern Cosmetics" (Cosmetics & Toiletries, Vol 97 Nov 1982 pp 85-88), Joel E Rogelberg "Dantogard: A New EPA Registered Preservative" (HAPPI, March 1986, pp. 60, 63-64), and M. Rosen, "A New Preservative: EPA Registered `Dantogard` Protects Water-Based Household, I&I Products from Microbial Contamination" (Soap/Cosmetics/Chemical Specialties, March 1986, pp. 28-29, 78). To broaden the spectrum of the microbial activities, these two classes of materials have been formulated together in a variety of different proportions (U.S. Pat. No. 4,496,576).
The availability of a solid form of 1,3-bis(hydroxymethyl)-5,5-dimethylhydantoin (DMDMH), its method of preparation, and its melt properties allow the preparation of virtually all combinations of parabens, at levels not possible with the commercial aqueous solutions of DMDMH. Unfortunately, the parabens have low water solubility and combinations with aqueous DMDMH solutions, for the purpose of providing broad spectrum preservatives, require large concentrations of compatibilizing materials; e.g., a stable combination of aqueous DMDMH with parabens, at a weight ratio of 30:10, requires over 50% by weight of propylene glycol.
This requirement of a significant amount of compatibilizing material naturally dilutes the activity of the concentrate, limits the flexibility of paraben/substituted dimethyl hydantoin formulation for optimum performance, and creates formulating incompatibilities.